A simple device for conveying a bundle of sheets is shown in British Pat. No. 1,559,898. This device only uses one pair of rollers.
A device for conveying a bundle of sheets using two pairs of rollers is shown in U.S. Pat. No. 3,076,196. The device described therein feeds sheets between a first pair of rollers and collects the sheets against an abutment which is disposed in the conveyor path past the rollers. The two rollers are spaced some distance apart so that the sheets can be pushed unobstructedly between the rollers and against the abutment. When the required sheets have been collected, the abutment is removed from the conveyor path and the two rollers, one of which is driven, are pressed against one another so that the resulting bundle of sheets is conveyed onto a second driven roller pair also disposed in the conveyor path. The rollers of the second pair are resiliently pressed against one another and are pressed apart by the bundle of sheets when the bundle is conveyed by the first pair of rollers into the nip of the second pair of rollers.
The disadvantage of this device is that when the bundle of sheets is relatively thick the leading edge of the bundle (top and/or bottom) collides with the surface of the second pair of rollers relatively far in front of the nip. As the bundle is conveyed on into the nip, the sheets of the bundle can readily shift with respect to one another and be conveyed on through the nip and deposited in that shifted condition. This problem may have adverse effects particularly if the sheets positioned between the first pair of rollers are stapled in one corner. The second pair of rollers may then cause the top or bottom sheets to take a skew position and subsequently form a sharp fold in the sheets or tear them at the staple as they pass through the second pair of rollers.
Another device for conveying a bundle of sheets is shown in U.S. Pat. No. 4,453,870. The device described therein also feeds sheets between two pairs of rollers and against a moveable gate which is disposed in the conveyor path past the first pair of rollers. Once the bundle of sheets has been formed against the moveable gate, the first pair of rollers is moved together, pressing on the sheets and forming a nip. When this is done, the rollers of the second pair are automatically set to a distance from one another which is equal to the distance between the rollers of the first pair when the nip is formed. The gate is then moved and the bundle of sheets is conveyed by the first pair of rollers to the second pair of rollers and then to the finishing station.
Like the device described in U.S. Pat. No. 3,076,196 one or both of the leading edges of the bundle of sheets collides with a roller of the second pair upon entering the nip with the possibility of the outer sheets of the bundle becoming shifted with respect to each other. Although the rollers of the second pair are separated from each other by a distance equal to the nip between the rollers of the first pair, this separation is not sufficient to prevent collision with the rollers. This is because the distance between the rollers of the first pair when forming the nip must be somewhat smaller than the thickness of the bundle of sheets to properly convey it.
A further disadvantage of this device is that the collection of a new bundle of sheets can only begin when the preceding bundle has completely passed through the second pair of rollers due to the direct linkage between the first and second pairs of rollers.
It would be desirable to provide a device without these disadvantages and one wherein the nip is formed only after the bundle of sheets has entered the nip forming space.